1. Oviposition by L. sericata has been induced on a moist clipped fleece by incorporating ammonium carbonate and indole, hence attraction is not completely dependent on some factor produced by the living animal.
2. Chemistry of attractants. A new method for determining small amounts of hydrogen sulphide is described. Larval excreta contains hydrogen sulphide but no indole or skatole. Following incubation the ammonia and sulphydryl contents of various natural attractants are markedly increased.
3. Field trials on sheep. 0·002% ethyl mercaptan in conjunction with 0·1% ammonium carbonate was able to induce oviposition by L. sericata. The mercaptan concentration could be reduced to 0·001%, providing 0·0001% hydrogen sulphide was present. 0·01% mercaptan and aqueous solutions of hydrogen sulphide alone are not attractive.
4. The results obtained support the hypothesis that attraction is the result of the breakdown of cystine, with the production of sulphur compounds, coupled with the presence of ammonium carbonate (or of some putrefactive material).
5. Chemical baits. During the period 17 August–21 September 1943, various combinations of ammonium carbonate, hydrogen sulphide and indole in conjunction with sheep wool proved to be attractants for females of L. caesar.